This invention relates to a coupling for a tube fitting, and in particular to an improved one-piece tubular male coupling in which a sleeve is held by a frangible connection to a nut. The invention particularly relates to improvements in the frangible connection so that said sleeve is deflected into a tube and sheared off into sealing engagement when the one-piece coupling engages a female coupling.
Tube fittings conventionally include a female coupling elment which has a passageway and is internally threaded, and such female coupling element is adjusted to be joined to a male coupling element which has a passageway and is externally threaded to engage the internal threads of the female coupling element. Such tube fittings also conventionally employ a sleeve between the coupling elements which is deflected inwardly when a nose of the sleeve contacts a camming surface in the passageway of the female coupling element. Such sleeve is deflected inwardly, and bites into sealing engagement with the wall of a tube which is inserted in the aligned passageways of the couplings.
A one-piece nut and sleeve element has been introduced in the art, and such sleeve is adapted to shear off from the nut and become attached to a tube when making up the fitting. It is desirable to form such one-piece nut and sleeve because the sleeve is then positively aligned with the body member of a male coupling element which, together with the female one-piece nut and sleeve coupling, forms the fitting. Additionally, a one-piece nut and sleeve coupling element prevents the sleeve from being installed backwardly in the fitting. An example of such a one-piece nut and sleeve is shown in U.S. Pat. No. 3,743,324, owned by the same assignee as herein identified. The assignee hereof commercially supplies one-piece nut and sleeve coupling elements under the trade designation "HI-DUTY", such couplings lead to improved installation of the fitting, as well as realizing other advantages, including economies in manufacturing a one-piece nut and sleeve construction.
Additional advantages are realized from such one-piece nut and sleeve coupling elements, for example, the nut portion guides the sleeve and prevents cocking until the deflectable nose portion of the sleeve has been substantially deflected into contact with the tube. Such sleeve is connected by a frangible connector to the nut, and this connector breaks only after the sleeve effectively contacts the tube.
The "HI-DUTY" coupling commercially supplied by the assignee identified herein includes a continuous interior shearing groove and a continuous exterior shearing groove axially spaced from the interior groove. The interior groove opens radially inwardly, while the exterior groove opens radially outwardly. A radial wall portion or web or break point separates the grooves, and this web is sheared as a result of normal fitting makeup forces.
It is required that the radial wall or connecting portion be axially thin to facilitate shearing during normal makeup of the fitting. Such shearing is reported by a "give" during normal makeup, and one or two additional turns completes the tightening of the fitting, including sealing engagement of the sleeve with the wall of the tube. Sufficient thinness of the connecting radial wall at the break point is required so that shearing results with normal makeup of the fitting. If such radial wall portion is too thick, then the sleeve will not shear at the desirable makeup forces.
Failure of the sleeve to shear in making up the fitting leads to certain recognized problems. One such problem is the rotation of the sleeve with the nut, thus failing to make the desired seal with the tube because of irregularities between the sidewall of the tube and the continuous biting edges of the sleeve. Another serious problem is the scarring or damage to the wall of the tube when disassembling the fittng and removing the nut with the still attached sleeve. The continuous edge of the sleeve will scar or scrub the wall of the tube in its linear travel.
It is therefore a continuing problem of manufacturing control to provide the connecting wall portion sufficiently thin to attain such desired shearing. Difficulties have been encountered in controlling tolerances so that the interior shear groove is desirably spaced axially relative to the exterior shearing groove.